Method and device for cleaning a molding surface of a reusable lens mold

ABSTRACT

A method for cleaning a molding surface ( 51 ) of a reusable lens mold ( 5 ), in particular of a reusable lens mold ( 5 ) for molding ophthalmic lenses such as soft contact lenses, comprising the steps of:
         generating a jet ( 3 ) of deionized water,   exposing the molding surface ( 51 ) of the reusable lens mold ( 5 ) to the jet ( 3 ) of deionized water,
 
wherein the jet ( 3 ) of deionized water has a circular full cone spray pattern and impinges on the molding surface ( 51 ) of the reusable lens mold ( 5 ), and wherein the circular full cone spray pattern has a uniform distribution of the volume flow of deionized water over the base of the cone of the circular full cone spray pattern.

This application is a division of U.S. patent application Ser. No.15/187,245, filed Jun. 20, 2016, which claims benefit under 35 U.S.C. §119(e) of U.S. provisional patent application No. 62/182,927, filed onJun. 22, 2015, whose disclosures are incorporated herein by reference inits entirety

FIELD OF THE INVENTION

The invention relates to a method for cleaning a molding surface of areusable lens mold, in particular of a reusable lens mold for moldingophthalmic lenses such as soft contact lenses. The invention alsorelates to an apparatus for carrying out the method.

BACKGROUND OF THE INVENTION

Mass production of ophthalmic lenses, in particular of contact lensessuch as soft contact lenses, is usually performed in a fully automatedprocess. In an embodiment of this fully automated process the softcontact lenses are manufactured with the aid of reusable moldscomprising male and female molds. In one processing station, a lensforming material is introduced into the female mold. Lens formingmaterials that may be useful in such process are, for example, lensforming materials based on polyvinyl alcohols (PVA) or lens formingmaterials based on silicone hydrogels (SiHy). After introduction of thelens forming material into the female mold, the female mold is mated ina subsequent processing station with a corresponding male mold to form amold cavity defining the shape of the soft contact lens to be formed. Ina yet further subsequent processing station, the lens forming materialwithin the mold cavity is polymerized and/or cross-linked, for exampleby irradiation with ultraviolet radiation (UV-radiation) to form thesoft contact lens.

The polymerization/cross-linking process by irradiation withUV-radiation may be performed using molds in which the mold cavity ofthe mated male and female molds is not completely sealed but isconnected by a small annular gap to a reservoir surrounding the moldcavity. During the polymerization/cross-linking process, excess lensforming material contained in the reservoir surrounding the mold cavityis allowed to flow from the reservoir through the small annular gap intothe mold cavity to compensate for a shrinkage in volume which may occurduring polymerization/cross-linking of the lens forming material withthe aid of UV-radiation. An annular metallic mask may be arranged at theradially outer boundary of the molding surface of the male mold.

The annular metallic mask, in particular a chromium mask which may havebeen applied to the male mold through deposition of a chromium coating,shields those portions of the lens forming material which are not to beexposed to UV-radiation, so that the mask accurately delimits the spacewhere the lens forming material enclosed between the mated male andfemale molds is exposed to UV-radiation to allow for a precisedefinition of the geometry of the lens edge of the soft contact lens tobe formed.

After exposure to UV-radiation, the mold is opened through separation ofthe male and female molds, the soft contact lens formed is removed fromthe male or female mold, respectively, and may subsequently betransported to additional processing stations.

Once the contact lens has been removed from the male or female mold, themolds used in the production of the soft contact lens are cleaned andrinsed through exposure to cleaning and rinsing liquid jets. Cleaningand rinsing liquids comprise, for example, water or water mixed withorganic solvents to remove from the used mold halves any debris such asresidual lens forming material adhering to the mold, as well asdeionized water for a final rinsing step. Thereafter, the cleaned andrinsed molds are dried in order to be ready for use in the nextproduction cycle.

As has been outlined above, mass production of ophthalmic lensesincludes the use of reusable molds. The reusable molds, or at leastthose parts thereof comprising the molding surfaces, are typically madefrom optically finished glass, for example quartz glass. Such reusablemolds are particularly advantageous since they are transparent toUV-radiation, they are durable, they can be cleaned and rinsed aftermolding of a soft contact lens for subsequent re-use, etc. Due to theoptical quality of the molding surfaces and the required accuracy of thechromium mask defining the geometry of the lens edge of the soft contactlens which is important for the wearing comfort, these molds or moldhalves are rather expensive.

As has been indicated, such molds are used in mass production of softcontact lenses so that they are used in very high numbers of subsequentproduction cycles before they are replaced. However, after such a highnumber of production cycles it may occur that the chromium mask mayslowly be degraded by the high number of cleaning and rinsing steps inwhich the chromium mask is exposed to the jets of deionized water. Aftera certain number of production cycles, it may occur that the mask isdegraded to an extent that the accuracy of the mask is no longersufficient to maintain the high level of accuracy required for the lensedge, so that the mold has to be replaced.

Due to the molds or mold halves being rather expensive, it is an objectof the invention to increase the number of production cycles the moldscan stand while maintaining the high level of accuracy required for thelens edge, and at the same time the molding surface of the mold halvesmust be reliably cleaned and rinsed before it is re-used.

SUMMARY OF THE INVENTION

These and other objects of the invention are achieved with a method andan apparatus as specified by the features of the respective independentclaims. Advantageous aspects of the method and apparatus according tothe invention are the subject of the dependent claims.

In accordance with the invention, the method for cleaning a moldingsurface of a reusable lens mold, in particular of a reusable lens moldfor molding ophthalmic lenses such as soft contact lenses, comprises thesteps of:

-   -   generating a jet of deionized water,    -   exposing the molding surface of the reusable lens mold to the        jet of deionized water,        wherein the jet of deionized water has a circular full cone        spray pattern and impinges on the molding surface of the        reusable lens mold, and wherein the circular full cone spray        pattern has a uniform distribution of the volume flow of        deionized water over the base of the cone of the circular full        cone spray pattern.

According to one aspect of the method according to the invention, thereusable lens mold comprises an annular metallic mask, in particular achromium mask, which is arranged at a radially outer boundary of themolding surface.

According to a further aspect of the method according to the invention,the reusable lens mold is transported through the jet of deionized wateralong a linear transport path.

According to a still further aspect of the method according to theinvention, a plurality of jets of deionized water are linearly arrangedat fixed locations, and wherein the reusable lens mold is transportedthrough the plurality of jets along the linear transport path whichextends along the linear arrangement of the plurality of jets.

According to yet a further aspect of the method according to theinvention, an apex of the molding surface of the reusable lens mold onone hand and a discharge orifice from which the jet of deionized waterhaving the full cone spray pattern is ejected on the other hand arearranged to be spaced by a predetermined impact distance.

According to a further aspect of the method according to the invention,the predetermined impact distance is in the range of 15 mm to 35 mm(millimeters).

In accordance with a further aspect of the method according to theinvention, the jet has a cone angle in the range of 80° to 100°.

In accordance with still a further aspect of the method according to theinvention, a flow rate of deionized water at a pressure of 4·10⁵ Pa isin the range of 0.40 l/min to 0.60 l/min (liters per minute).

In accordance with yet a further aspect of the method according to theinvention, the jet is generated with the aid of a full cone nozzle.

According to a further aspect of the method according to the invention,the reusable lens mold is transported along the linear transport path ata velocity in the range of 100 mm/s to 200 mm/s (millimeters persecond).

According to a still further aspect of the method according to theinvention, the individual jets of the plurality of linearly arrangedjets are arranged in a manner such that the impact areas of adjacentlyarranged individual jets do not overlap at the predetermined impactdistance.

Also in accordance with the invention, the apparatus for cleaning amolding surface of a reusable lens mold, in particular of a reusablelens mold for molding ophthalmic lenses such as soft contact lenses,comprises:

-   -   at least one full cone nozzle for generating a jet of deionized        water having a circular full cone spray pattern having a uniform        distribution of the volume flow of deionized water over the base        of the cone of the circular full cone spray pattern,    -   a positioning device for arranging the reusable lens mold        relative to the full cone nozzle such that the molding surface        of the reusable lens mold is exposed to the jet of deionized        water.

According to one aspect of the apparatus according to the invention, aplurality of full cone nozzles are linearly arranged at fixed locations,and the positioning device comprises a transportation device forlinearly transporting the reusable lens mold along a linear transportpath which extends along the plurality of linearly arranged full conenozzles.

According to a further aspect of the apparatus according to theinvention, the discharge orifice of the respective individual full conenozzle of the plurality of linearly arranged full cone nozzles on onehand and the apex of the molding surface of the reusable lens mold onthe other hand are arranged at a predetermined impact distance. Theindividual full cone nozzles of the plurality of linearly arranged fullcone nozzles are arranged such that in operation the circular full conespray patterns of the individual full cone nozzles of the linearlyarranged full cone nozzles do not overlap at the predetermined impactdistance.

It is to be noted that generally, that generally any of afore-describedfeatures or aspects of the invention can be combined with any otherafore-described feature or aspect of the invention as long as suchcombination is not mutually exclusive.

The circular full cone spray pattern, as its name says, has the shape ofa cone having a circular base. The afore-described uniform distributionof the volume flow of deionized water over the base of the cone of thecircular full cone spray pattern allows for a reliable cleaning/rinsingof the mold on one hand while at the same time enhancing the number ofproduction cycles the mold can stand before it must be replaced.Therefore, a considerably higher number of lenses having lens edges of ahigh level of accuracy can be produced with the mold, in particular whenusing a re-usable mold having an annular metallic mask arranged thereonto define the geometry of the lens edge. The circular full cone spraypattern is a pattern that has the shape of a cone having a circularbase. A uniform distribution of the volume flow over the base of thecone of the full cone spray pattern in this connection means that thevariation of the volume flow over the base of the cone of the full conespray pattern is less than 15%. Reusable molds are typically made of anoptically finished glass, for example quartz glass. While generally themethod and apparatus according to the invention can also be used for amold not having a metallic mask applied thereto, they are particularlysuitable for a mold having such metallic mask applied thereto, inparticular a chromium mask. The uniform distribution of the volume flowof deionized water of the circular full cone spray pattern leads to agentle and a the same time effective cleaning and rinsing of the moldingsurface of the mold as well as to a significantly reduced degradation ofthe chromium mask when compared to other spray patterns. Circular fullcone spray patterns may advantageously be generated using full conenozzles (for example axial-flow full cone nozzles or tangential-flowfull cone nozzles) which are available on the market.

To render the method and apparatus according to the invention even moreeffective, on or more molds can be transported through one or more jetsof deionized water, and in case of a plurality of jets are present thesemay be linearly arranged at fixed locations along a linear transportpath, so that each mold is transported through the individual jets ofdeionized water when being transported along the linear transport path.Advantageously, the individual jets are arranged in a manner such thatthey do not overlap when the apex of the molding surface of the mold isarranged at a predetermined impact distance which is the distancebetween a discharge orifice from which the individual jet is ejected andthe apex of the molding surface of the mold. Such impact distance may,for example, be in the range of 15 mm to 35 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous aspects of the invention become apparent from thefollowing description of embodiments of the invention with the aid ofthe drawings in which:

FIG. 1 is a schematic view of essential components of an embodiment ofan apparatus according to the invention comprising a plurality oflinearly arranged full cone nozzles, and a male mold being arranged at apredetermined impact distance relative to the discharge orifice of thefull cone nozzles,

FIG. 2 is a schematic representation of an embodiment of a full conenozzle suitable for the apparatus and method according to the invention,

FIG. 3 is a partial longitudinal section of the full cone nozzle shownin FIG. 2, and

FIG. 4 is a longitudinal section of another embodiment of a full conenozzle suitable for the apparatus and method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows essential components of an embodiment of an apparatusaccording to the invention for cleaning a molding surface 51 of areusable lens mold 5, in the embodiment shown of a reusable male mold 5for molding an ophthalmic lens such as a soft contact lens. Theapparatus comprises a spray system 1 comprising a plurality of linearlyarranged full cone nozzles 2, in the embodiment shown in FIG. 1 foursuch full cone nozzles 2 are shown by way of example. The full conenozzles 2 are preferably of the type axial-flow full cone nozzle and areavailable from the company Lechler GmbH, Ulmer Str. 128, DE-72555Metzingen, Germany, although alternatively nozzles of the typetangential-flow full cone nozzle may be used as well. The reusable malemold 5 shown in FIG. 1 comprises an annular metallic mask 52 (e.g.chromium mask) arranged at and/or forming the radially outer boundary ofa molding surface 51 of the reusable male mold 5.

The reusable male mold 5 shown in FIG. 1 has been used in a soft contactlens molding process and must now be cleaned and dried before it can bere-used for molding the next lens. Cleaning of the male mold 5 maycomprise several cleaning steps and a final rinsing step in which themale mold 5 is exposed to deionized water after it has been cleaned inone or more preceding cleaning steps in which liquids other thandeionized water are typically used which are less aggressive to thechromium mask than is deionized water. However, at least in the finalrinsing step deionized water is used. After the final rinsing step, themold is dried and is ready for being reused.

For the final rinsing step, the reusable male mold 5 is transported tothe spray system 1 comprising the plurality of linearly arranged fullcone nozzles 2. Similarly, the corresponding reusable female mold may becleaned/rinsed in a similar manner (although not being provided with achromium mask). For the sake of simplicity in the following only thecleaning/rinsing of the reusable male mold 5 comprising the chromiummask 52 will be described in more detail making reference to the finalrinsing step in which deionized water is used. In the embodiment shownin FIG. 1, the full cone nozzles 2 of the spray system 1 are linearlyarranged at fixed locations along a common supply pipe 4 and areconnected to the common supply pipe 4 to in operation generate fourindividual jets 3 of deionized water. Each individual jet 3 of deionizedwater has a circular full cone spray pattern as can be seen from FIG. 1in which the base of the cone is also indicated schematically. As thereusable male mold 5 is transported (using a suitable transportationdevice, not shown) along a linear transport path (indicated by the arrowshown in FIG. 1) which extends along the linearly arranged full conenozzles 2, the molding surface 51 bounded by the chromium mask 52 of thereusable male mold 5 is successively impacted by the jets 3 of deionizedwater ejected from the full cone nozzles 2. The (lateral) distancebetween the discharging orifices 23 of adjacently arranged full conenozzles 2 may, for example, be in the range of 30 mm to 60 mm, and mayin particular be 40 mm. Transportation of the reusable male mold 5 maybe performed at a velocity in the range of 100 mm/s to 200 mm/s, forexample this velocity may be 180 mm/s.

The jet 3 created by the respective individual full cone nozzles 2preferably has a cone angle α which may, for example, be in the range of80° to 100°, and may in particular be 90°. The impact distance d (FIG.1), that is to say the distance between the discharge orifice 23 (seeFIG. 3) of the full cone nozzle 2 and the apex of the molding surface 51of the reusable male mold 5 may generally be in the range of 15 mm to 25mm, more particularly in the range of 15 mm to 25 mm, and may in forexample be 22.5 mm. By way of example, the flow rate of deionized waterthrough the individual full cone nozzles 2 at a pressure of 4·10⁵ Pa(corresponding to a pressure of 4 bars) may be in the range of 0.40l/min (liters per minute) to 0.60 l/min. By way of example, too, thedeionized water may be supplied to the respective full cone nozzles 2 ata pressure which is in the range of 1·10⁵ Pa to 6·10⁵ Pa (correspondingto 1 to 6 bars), particularly at a pressure of 2.5·10⁵ Pa (2.5 bars). Inparticular, the amount of liquid per area and per minute may be selectedto be smaller than 1 ml per minute and per square millimeter (1ml/min·mm²) at a pressure of 4 bars and at an impact distance of 15 mm.

As has been mentioned already, in operation the full cone nozzles 2 areembodied to generate a uniform distribution of the volume flow ofdeionized water over the base of the cone of the circular full conespray pattern, so that for example the variation of the volume flow overthe entire impact area may be less than 10%. As can be seen from FIG. 1,the full cone nozzles 2 are arranged such that the circular full conespray patterns generated by adjacently arranged full cone nozzles 2 donot overlap when the mold surface 51 of the male mold 5 is arranged atthe above-described impact distance d.

A first embodiment of a full cone nozzle 2 suitable for the apparatusand method according to the invention is shown in FIG. 2 and FIG. 3.This embodiment of the full cone nozzle 2 comprises an elongated hollownozzle body 21 comprising at one end thereof a radially outwardlyprojecting flange 22, so that with the aid of a retainer nut 220 thenozzle 2 can be screw-mounted onto a connecting spout 41 which in turnis connected (e.g. welded) to the common supply pipe 4.

FIG. 4 shows a second embodiment of a full cone nozzle 2 which may beprovided with a thread on the outer surface of the nozzle body so thatit can be directly screw-mounted to the connecting spout 41 which inturn is connected to the common supply pipe 4. A hex head 28 is providedon the nozzle body allowing for wrench tightening of the full conenozzle 2 during screw-mounting the nozzle 2 to the connecting spout 41.

The embodiments of the full cone nozzles shown in FIG. 2, FIG. 3, andFIG. 4 allow for an easy replacement, if necessary. In the full conenozzles 2 shown in FIG. 2, FIG. 3 and FIG. 4, the elongated hollownozzle body 21 has an axial liquid passageway 24 for communicating withthe spout 41. At the discharge orifice 23 located at the downstream endof the nozzle body 21 the full cone nozzle 2 comprises an outwardlyextending frustoconical section 25.

Axial-flow full cone nozzles are of the type turbulence nozzle. In aturbulence nozzle, the deionized water rotates through a chamber 27while proceeding to the discharge orifice 23 of the full cone liquidnozzle 2. Thus, the jet 3 ejected from the discharge orifice has thedesired full cone spray pattern.

In the particular case of an axial-flow full cone nozzle 2 shown inlongitudinal section in FIG. 3 and FIG. 4, one or more vanes 26 arearranged in the passageway 24 between the upstream end of the nozzlebody 21 and the discharge orifice 23 of the full cone liquid nozzle 2.The one or more vanes 26 arranged in the nozzle body 21 impart aswirling movement to the deionized water passing through the nozzle body21 and breaks up the deionized water flow into liquid droplets which areuniformly distributed over the base of the full cone spray pattern ofthe jet 3 emitted from the discharge orifice 23 of the full cone liquidnozzle 2. The full cone liquid nozzle 2 thus creates a very uniformliquid spray pattern which is superior to the uniformity of conventionalspray nozzles, for example flat jet nozzles.

Other nozzle types are suitable for the generation of a circular fullcone spray pattern having a uniform distribution of the volume flow ofdeionized water over the base of the cone as well such as, for example,tangential-flow full cone nozzles. In a tangential-flow full conenozzle, the deionized water is typically supplied tangentially to aswirl chamber. Suitable tangential-flow full cone nozzles are availablefrom the company Lechler GmbH, Ulmer Str. 128, DE-72555 Metzingen,Germany, as well.

In operation, in the embodiment illustrated in FIG. 1 the individualjets 3 of deionized water having the full cone spray pattern are ejectedfrom the full cone nozzles 2, with the full cone spray pattern having acone angle α which is preferably between 80° and 100°, and isparticularly 90°. As indicated previously, the full cone liquid nozzles2 are arranged such that the jets of adjacently arranged full conenozzles 2 do not overlap at the impact distance d.

By way of example, the full cone nozzle 2 may be made of PVDF(polyvinylidene fluoride), brass, Hastelloy®, Titanium or stainlesssteel, or of suitable thermoplastic polymeric materials such as, forexample, PVC (polyvinyl chloride), polypropylene or Teflon®.

Although the invention has been described with the aid of specificembodiments, it is evident to the person skilled in the art that thisembodiment has been described by way of example only and that variouschanges and modifications are conceivable without departing from theteaching underlying the invention. Therefore, the scope of protection isnot intended to be limited by the embodiments described, but rather isdefined by the appended claims.

The invention claimed is:
 1. Apparatus for cleaning a molding surface of a reusable lens mold for molding soft contact lenses, the apparatus comprising: at least one full cone nozzle for generating a jet of deionized water having a circular full cone spray pattern having a uniform distribution of the volume flow of deionized water, wherein the shape of a cone having a circular base, a positioning device for arranging the reusable lens mold relative to the full cone nozzle such that the molding surface of the reusable lens mold is exposed to the jet of deionized water.
 2. Apparatus according to claim 1, wherein a plurality of full cone nozzles are linearly arranged at fixed locations, and wherein the positioning device comprises a transportation device for linearly transporting the reusable lens mold along a linear transport path which extends along the plurality of linearly arranged full cone nozzles.
 3. Apparatus according to claim 2, wherein a discharge orifice of the respective individual full cone nozzle of the plurality of linearly arranged full cone nozzles and the apex of the molding surface of the reusable lens mold are arranged at a predetermined impact distance (d), and wherein the individual full cone nozzles of the plurality of linearly arranged full cone nozzles are arranged such that in operation the circular full cone spray patterns of the individual full cone nozzles of the linearly arranged full cone nozzles do not overlap at the predetermined impact distance (d). 